Semiconductors, such as integrated circuits, are formed on wafers which are then cut into dice or chips that individually may be mounted on substrates. Typically, the substrate is electrically and thermally conductive, with mounting providing both good electrical and good thermal conductivity between the die and the substrate.
Known methods of attaching a die to an electrically and thermally conductive substrate include employing a solder or eutectic alloy such as a gold-silicon alloy, employing die-attach adhesive pastes consisting of a heat-curing epoxy resin composition filled with fine metal particles; and employing an electrically and thermally conductive adhesive transfer tape which comprises a flexible, carrier web to which is lightly adhered an adhesive containing fine metal particles or a deformable metal foil. See, for example, U.S. Pat. No. 4,606,962. Precious metal eutectic alloy connections may be prohibitively expensive and particle or foil adhesive connections experience problems discussed below.
Semiconductor chips are used in a myriad of applications ranging from, for example, the dash board of an automobile, to pocket calculators, to space vehicles. In many of these various applications temperatures can range from well below 0.degree. C. to well above 150.degree. C. In the case of prior art adhesives containing particles or foils, as temperatures vary the adhesive used to connect the chip to the substrate expands and contracts. The metal particles or foil used to make electrical connection between the chip and substrate also expands and contracts, but at a greatly different rate from that of the adhesives typically used. Therefore, as temperature changes, electrical connection can be lost as the adhesive expands or contracts at a rate different from that of the metal. This can result in the failure of the part to which the chip was connected, in some cases with drastic consequences. Similarly, failure can occur with the use of solder as differential expansion causes the chip to crack.
There are other various applications where a flexible composite capable of joining two members electrically and thermally throughout extremes in temperature is required. Examples of these applications include conductive gaskets and floor mats which eliminate static.
It is therefore highly desirable to provide a flexible composite which does not experience a loss of electrical or thermal connection when exposed to extreme temperature variations, by providing a conductive flexible composite which includes a resilient structured conductive layer.